This has happened to me after a 20 year career and successful side business. Instead of fight it, I accept it and look at it as a natural part of growth, not stagnation. It opens up the possibility for you to take your job for what it is—a job—and explore new hobbies and interests.
If nothing is interesting, take a break from trying and play video games or watch tv for a year. Youre going to bump up against a lot of potential interests, and one might naturally take off.
For me, that new interest has been electronic music production. And I don’t follow any predefined path. Instead, I just go in the direction it takes me. For now, that’s been developing 4 bar loops and hoarding gear. Those are the antithesis of a productive producer.
But I remember how I got started in software collecting warez and keygens without any real rhyme or reason. That lead to me wanting to know how software was cracked, built, then how businesses and careers were built, learned a lot about leadership as a byproduct of having a career, etc.
So, while it might sound cliche, open your mind and follow your heart and don’t be too hard on yourself. It’s ok to relax, breathe, and enjoy the life you’ve carved out for yourself so far.